LCGB Forums

I'm about to get a GP200 barrel re-bored and an oversize piston fitted,what i'd like to know is-
a.What is the piston to barrel clearance
b.how much clearance before you get piston slap
c.what does piston slap sound like.The engine rattles badly at the moment and it all seems to be coming from the top end,the small end bearing is new so I dont think its that.
Any help would be greatfully received.

Paul

As a rule the chap who does the re bore will supply the correct piston or give you the exact size. Depends on what make you want, Hepolite used to make v/good pistons.
Colin

I have a piston,a 66.2 Mahle three ring,its one that I bought from SR a while back
Paul

My standard TV200 is running about 6.5 thou. and it does rattle a bit when cold, but still goes ok. This isn`t by design just seized it, by the time the barrel had been cleaned up just fitted a new piston, just as a stopgap until its done properly. About 4 - 4.5 thou. should be ok.

The clearance is normally factored into the piston so if you want to run the standard clearance for that piston it is normal to bore and hone the barrel to the size on the piston.
Then check clearances.

If you want extra clearance ask for it to be bored to size then hone it out for the extra clearance.

The standard piston clearances are given in the Lambretta Workshop Manual, which also includes the ring end gaps.
All these measurements are given in metric.

From experience standard 200 barrels do not like to run at less than 2 1/2 thou of an inch clearance.

Good advice from the Cap'n as always. I prefer a 3 thou piston to barrel clearance, but was assured by a local tuner that I needed a 4 thou clearance. My Indian GP 200 barrel now runs this clearance with no problems.